Method And Apparatus For Controlling Adaptive Circuits

ABSTRACT

A feed-forward amplifier having a signal cancellation loop including a cancellation node that includes a gain controller and a phase controller. Each controller provides a discrete tap steering signal and modulates the corresponding tap steering signal with a discrete tracer signal that takes on a preselected sequence of values. The sequence chosen so that the tracer signal is mutually orthogonal to each other tracer signal over a preselected period. A gain and phase adjuster connected to the outputs of the controllers provides a controlled gain change and phase shift in the signal cancellation loop, the magnitude of the gain change and phase shift controlled by the corresponding tap steering signals presented to the gain and phase adjuster by the controllers. A detector, the input of which is connected to the cancellation node and the output of which is connected to the controllers, outputs a measure of the envelope of the signal at the cancellation node. After the preselected period new values for the tap steering signals presented to the gain and phase adjuster by the controllers are obtained by multiplying detector output by the respective tracer signal, each over the respective preselected period, summing each resulting series of values, and changing the tap steering signals to be modulated and presented to the gain and phase adjuster in accordance with the values of the respective sums.

The present application is a divisional of U.S. patent application Ser.No. 10/486,792, filed Oct. 4, 2004, which is a 371 of PCT/US02/25557,filed Aug. 12, 2002, which claims benefit of U.S. ProvisionalApplication No. 60/311,358, filed Aug. 13, 2001, and is a CIP of U.S.patent application Ser. No. 10/016,691, filed Dec. 17, 2001, now U.S.Pat. No. 6,614,298, the contents of all of which are incorporated hereinby reference.

FIELD OF THE INVENTION

The present invention relates to adaptive circuits. More specifically,the present invention relates to an apparatus and method for controllingadaptive circuits, such as controlling gain and phase adjustments in afeed forward amplifier circuit.

BACKGROUND OF THE INVENTION

Adaptive circuits are well known and used in a variety of applications.One well-known example of an adaptive circuit is the feed forwardamplifier (“FFA”). In order to achieve linearity in a feed forwardamplifier, careful control of the amplifier circuitry is required. Inparticular, in FFAs two or more gain and phase adjusters are oftenemployed and the taps of each of these adjusters are carefully steeredto achieve linearity through the amplifier.

Within the art of FFAs, it is known to use detector-controller circuits,one for each gain-and-phase adjuster. Each detector-controller circuitis operable to steer the taps of its respective gain-and-phase adjusterin the FFA so that the main amplifier and correctional amplifier canproperly cooperate in order to reduce error introduced by the mainamplifier and, should a pilot tone be used in the FFA, to also reducethe output residue of the pilot tone injected prior to the mainamplifier.

In certain prior art detector-controller circuits, once the detectorportion of the detector-controller circuit has indicated that theassociated controller portion should make an adjustment, the controllerarbitrarily steers the taps of the gain-and-phase adjuster in adirection to either increase or decrease the input to the tap, withoutknowing which of an increase or decrease will actually achieve thedesired effect. In order to verify whether the controller steered thetap in the correct direction (e.g., to increase the signal to the tap),after the correction has been applied the detector circuit ascertainswhether the direction of the variation brought about the desired effect,and, if so, instructs the controller circuit to continue steering in thesame direction, if necessary. If, however, the detector circuitascertains that the steering direction brought about an undesiredresult, then the detector instructs to the controller to try steeringthe tap in the opposite direction (e.g., to decrease the signal to thetap).

In the prior art, each detector-controller circuit works independentlyof each other, and therefore, achieving convergence towards an optimumlevel for each tap of each adjuster can be difficult. For example, rapidchanges in the strength of the input signal being amplified by the FFAcan make it difficult for the detector-controller circuits to respondquickly enough to converge the tap levels of each gain-and-phaseadjuster towards the respective optimum levels. Furthermore, theadjustment of one tap of a gain-and-phase adjuster can disrupt anoptimum or near optimum input level achieved at another tap, thereforecascading disruptions through all of the taps.

The inventor of the present invention also believes that a furtherproblem is that such prior art controller circuits can sometimes resultin taps being steered to levels that are levels corresponding to localminima for the input signal, missing a global optimum for the inputsignal.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a novel apparatusand method for controlling an adaptive circuit that obviates ormitigates at least one of the above-identified disadvantages of theprior art. It is a further object of the present invention to provide anovel feed forward amplifier that obviates or mitigates at least one ofthe above-identified disadvantages of the prior art.

According to an aspect of the present invention, there is provided afeed-forward amplifier having a signal cancellation loop including acancellation node that includes a gain controller and a phasecontroller. Each controller provides a discrete tap steering signal andmodulates the corresponding tap steering signal with a discrete tracersignal that takes on a preselected sequence of values. The sequence ischosen so that the tracer signal is mutually orthogonal to each othertracer signal over a preselected period. A gain and phase adjusterconnected to the outputs of the controllers provides a controlled gainchange and phase shift in the signal cancellation loop, the magnitude ofthe gain change and phase shift controlled by the corresponding tapsteering signals presented to the gain and phase adjuster by thecontrollers. A detector, the input of which is connected to thecancellation node and the output of which is connected to thecontrollers, outputs a measure of the envelope of the signal at thecancellation node. After the preselected period new values for the tapsteering signals presented to the gain and phase adjuster by thecontrollers are obtained by multiplying detector output by therespective tracer signal, each over the respective preselected period,summing each resulting series of values, and changing the tap steeringsignals to be modulated and presented to the gain and phase adjuster inaccordance with the values of the respective sums. Optionally, each tapsteering signal may be increased or decreased depending upon thepolarity of the corresponding sum, or the tap steering signal presentedto the gain and phase adjuster is left unchanged if the correspondingsum is zero or within a preselected range about zero but, if thecorresponding sum is outside the preselected range about zero, isincreased or decreased depending upon the polarity of the correspondingsum. Also, each tap steering signal is increased if the correspondingsum is positive and decreased if the corresponding sum is negative. Inany of the embodiments discussed above, the tracer signals vary inpolarity but not in magnitude and may be chosen to be pseudo noisesequences or Walsh codes.

According to another aspect of the present invention, there is provideda feed-forward amplifier that includes:

an input port;

a first main path splitter, the input of which is connected to the inputport so that when an input signal applied to the input port it is splitby the first main path splitter into a main signal and a feed-forwardsignal;

a main signal path gain and phase adjuster, the input of which isconnected to the first output of the first main path splitter, the mainsignal path gain and phase adjuster having a gain-control input tap anda phase-control input tap configured so that the voltage levels on thetaps control the amplitude and phase of the main signal;

a main amplifier, the input of which is connected to the output of themain signal path gain and phase adjuster;

a second main path splitter, the input of which is connected to theoutput of the main amplifier;

a feed-forward signal path delay element, the input of which isconnected to the second output of the first main path splitter, thedelay imposed by the feed-forward signal path delay element selected toapproximately match the delay in the main signal caused by the mainamplifier;

a feed-forward path coupler, the first input of which is connected tothe output of the feed-forward signal path delay element;

a connector/attenuator connecting the second output of the second mainpath splitter to the second input of the feed-forward path coupler, theattenuation selected so that the undistorted portion of the main signalprovided to the feed-forward path coupler is approximately cancelled outby the feed-forward signal;

a feed-forward path splitter, the input of which is connected to theoutput of the feed-forward path coupler;

a detector, the input of which is connected to the second output of thefeed-forward path splitter;

a gain controller, the input of which is connected to the output of thedetector and the output of which is connected to the gain-control inputtap; and

a phase controller, the input of which is connected to the output of thedetector and the output of which is connected to the phase-control inputtap,

wherein:

each of the controllers modulates the voltage level on its respectiveoutput with a discrete low level signal that takes on a preselectedsequence of values, the sequence chosen so that each low level signal ismutually orthogonal to each other low level signal over a preselectedperiod; the detector outputs a measure of the envelope of the signal atthe cancellation node; and each controller multiples the signal receivedfrom the detector by the low level signal with which it modulated thetap to which it is connected, in each case over the preselected period,sums the resulting series of values over time, and changes the voltagelevel on its respective tap in accordance with the value of the sum.

Optionally, each voltage level is increased or decreased depending uponthe polarity of the corresponding sum or the voltage level presented tothe gain and phase adjuster is left unchanged if the corresponding sumis zero or within a preselected range about zero but, if thecorresponding sum is outside the preselected range about zero, isincreased or decreased depending upon the polarity of the correspondingsum. Also, each voltage level may be increased if the corresponding sumis positive and decreased if the corresponding sum is negative and eachoutput voltage level may be changed in proportion to magnitude of therespective sum.

In any of the embodiments discussed above, the low level signals vary inpolarity but not in magnitude and the low level signals may be chosen tobe pseudo noise sequences or Walsh codes.

According to yet another aspect of the present invention, there isprovided a feed-forward amplifier having a signal cancellation loopincluding a cancellation node at which a signal is to be minimized,including:

a controller for providing a tap steering signal and modulating the tapsteering signal with a tracer signal that takes on a preselectedsequence of values;

an adjuster connected to the output of the controller for providing acontrolled change in a characteristic of the signal cancellation loopthat results in a change in a measure of the envelope of the signal atthe cancellation node, the magnitude of the change in the characteristiccontrolled by the modulated tap steering signal presented to theadjuster by the controller; and

a detector, the input of which is connected to the cancellation node andthe output of which is connected to the controller, the detector foroutputting the measure of the envelope of the signal at the cancellationnode,

wherein after the preselected period a new setting for the tap steeringsignal is obtained by multiplying the detector output by the tracersignal, summing the resulting series of values, and changing the tapsteering signal to be modulated and provided to the adjuster inaccordance with the value of the sum.

Optionally, the tap steering signal may be increased or decreaseddepending upon the polarity of the corresponding sum, or the tapsteering signal presented to the gain and phase adjuster is leftunchanged if the corresponding sum is zero or within a preselected rangeabout zero but, if the corresponding sum is outside the preselectedrange about zero, is increased or decreased depending upon the polarityof the corresponding sum. Also, the tap steering signal is increased ifthe corresponding sum is positive and decreased if the corresponding sumis negative. In any of the embodiments discussed above, the tracersignal vary in polarity but not in magnitude and may be chosen to bepseudo noise sequences or Walsh codes.

According to yet another aspect of the present invention, there isprovided a circuit having a node at which a signal is adaptivelyminimized by the circuit, comprising: a controller providing an outputvoltage level, the output voltage level modulated by a low level signalthat takes on a preselected sequence of values over a preselectedperiod; an adjuster connected to the output of the controller forproviding a controlled change in a characteristic of the adaptivecircuit that results in a change in a measure of the envelope of thesignal at the node, the magnitude of the change in the characteristiccontrolled by the voltage level presented to the adjuster by thecontroller; and a detector, the input of which is connected to the nodeand the output of which is connected to the controller, the detectoroutputting the measure of the envelope of the signal at the node,wherein after the preselected period a new setting for the voltage levelpresented to the adjuster by the controller is obtained by multiplyingthe detector output by the low level signal, summing the resultingseries of values, and changing the voltage level presented to theadjuster in accordance with the value of the sum.

Optionally, each voltage level is increased or decreased depending uponthe polarity of the corresponding sum or the voltage level presented tothe adjuster is left unchanged if the corresponding sum is zero orwithin a preselected range about zero but, if the corresponding sum isoutside the preselected range about zero, is increased or decreaseddepending upon the polarity of the corresponding sum. Also, each voltagelevel may be increased if the corresponding sum is positive anddecreased if the corresponding sum is negative and each output voltagelevel may be changed in proportion to magnitude of the respective sum.

According to yet another aspect of the present invention, there isprovided a feed forward amplifier comprising:

an amplifier portion including a coupler, first and second gain andphase adjusters, first and second delay elements, a main amplifier and acorrectional amplifier, the coupler providing an input signal to saidamplifier portion to a first signal path including the first gain andphase adjuster, the main amplifier and the first delay element and anoutput and the coupler providing the input signal to a second signalpath including the second delay element, the second gain and phaseadjuster and the correctional amplifier having a first signal path forcarrying an input signal to a first gain-and-phase adjuster and amain-amplifier, said first gain-and-phase adjuster having a pair of tapsfor steering said first adjuster, said amplifier portion having a secondsignal path for carrying a sample of said input signal generated to asecond gain-and-phase adjuster and a correctional-amplifier, said secondgain-and-phase adjuster having a pair of taps for steering saidadjuster; and

a detector-controller portion having a first detector for receiving adetected signal from said first signal path and a second detector forreceiving a detected signal from said second signal path, saiddetector-controller portion further comprising a first pair ofcontrollers for receiving said detected signal from said first detectorand a second pair of controllers for receiving said detected signal fromsaid second detector, said controllers each operable to steer arespective one of said taps based on said received detected signals,each of said controllers further operable to inject tracer-signals intoits respective tap, said tracer-signals for carrying through saidamplifier portion and modulating said detected signals, said controllerseach operable to extract from its respective detected signals atap-signal by using its respective said tracer-signal, said controllerseach further operable to utilize said extracted tap-signal to determinea desired direction for steering its respective tap and to output,substantially simultaneously with each other controller, a signal tosteer said respective tap.

According to yet another aspect of the present invention, there isprovided a feed forward amplifier comprising:

an amplifier portion including:

(a) a first signal path having a first gain and phase adjuster, a mainamplifier and a delay element; and

(b) a second signal path having a delay element, a second gain and phaseadjuster and a correctional amplifier, each gain and phase adjusterincluding a control input tap to accept an input to alter the phaseresponse of the gain and phase adjuster and a control input tap toaccept an input to alter the gain response of the gain and phaseadjuster, the first and second signal paths having a common signal inputand a common signal output; and

a detector portion including:

(c) a first detector to receive a signal from the common signal outputand to provide the received signal to a first controller operable tocreate an input to the gain tap of the second gain and phase adjusterand to provide the received signal to a second controller operable tocreate an input to the phase tap of the second gain and phase adjuster;and

(d) a second detector to receive a signal from the second signal pathbefore the second gain and phase adjuster and to provide the receivedsignal to a first controller operable to create an input to the gain tapof the first gain and phase adjuster and to provide the received signalto a second controller operable to create an input to the phase tap ofthe first gain and phase adjuster, each controller responsive to acomponent in said received signals which is orthogonal to the componentsto which each other controller are responsive to and all the createdinputs being applied to the taps substantially simultaneously andaltering the operation of said feed forward amplifier to linearize theamplification of the input signal through the feed forward amplifier.

According to yet another aspect of the present invention, there isprovided a method for operating an adaptive control circuit having aplurality of control input taps, said method comprising, for each saidcontrol input, the steps of: detecting a signal, including a tracersignal, from said circuit; extracting a measurement from the tracersignal in said detected signal; determining an appropriate input to beapplied to said control input to improve operation of said adaptivecircuit; creating a tracer signal for said control input, said createdtracer signal being orthogonal to the tracer signals created for eachother control input; and combining said tracer signal and saiddetermined input and applying the resulting signal to said controlinput.

An apparatus and method for operating an adaptive circuit includesinjecting a set of orthogonal tracer signals into the circuit. Thetracers' signals are extracted after modification during operation of atleast a portion of the circuit and are examined by respectivecontrollers to modify operation of the circuit.

In one embodiment, the invention is incorporated into a feed forwardamplifier in which a set of orthogonal tracer signals is applied to theamplifier. A detector controller detects a signal including ascomponents the orthogonal tracer signals as modified by portions of theamplifier. Each controller portion of the detector controller extracts ameasurement relative to its respective tracer signal from the detectedsignal and modifies its output to control a portion of the amplifieraccordingly. The controllers apply their outputs to the respectiveportions of the amplifier at substantially the same time, leading toquick convergence of the operating point of the amplifier to an optimal,or near-optimal, configuration. Injection of the tracer signals into theamplifier is accomplished by dithering the controller outputs by therespective orthogonal tracer signals.

According to yet another aspect of the present invention, there isprovided an adaptive circuit comprising:

at least two adjusters, each adjuster including at least one controlinput to alter the operation of the circuit;

at least one signal generator to create at least one tracer signal, eachcreated tracer signal being orthogonal to each other created tracersignal;

at least two controllers, each controller operable to output a controlsignal to at least a respective one of the control inputs of the atleast two adjusters, a different orthogonal tracer signal from said atleast one signal generator being applied to each respective controlsignal as a dither; and

at least one detector operable to extract a composite signal from thecircuit and to apply the composite signal to the at least twocontrollers, each controller being responsive to the applied signal toextract at least one orthogonal tracer and alter the respective controlsignal to converge operation of the circuit to an optimal or nearoptimal configuration.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the present invention will now be described, byway of example only, with reference to the attached Figures, wherein:

FIG. 1 is a block diagram of a feed forward amplifier in accordance withan embodiment of the present invention;

FIG. 2 is a block diagram of a detector-controller portion of theamplifier shown in FIG. 1;

FIG. 3 is a flow chart showing a method of controlling the gain andphase adjustment of the amplifier of FIG. 1;

FIG. 4 is an exemplary set of Walsh codes for use in thedetector-controller portion of the amplifier of FIGS. 1 and 2;

FIG. 5 shows an example of the operation of two of the controllers shownin FIG. 2 using the method of FIG. 3, during an initial power-on of theamplifier of FIG. 1; and

FIG. 6 shows an example of the operation of the controllers shown inFIG. 5 during a subsequent iteration through the method shown of FIG. 3.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to FIG. 1, a forward feed amplifier (“FFA”) in accordancewith an embodiment of the invention is indicated generally at 20. FFA 20comprises an amplifier portion 24 and a detector-controller portion 28.Amplifier portion 24 includes a coupler 36 that is connected to an inputsignal path 40. Coupler 36 is operable to split an incoming signal frompath 40 into a main amplifier signal path 44 and a correctionalamplifier signal path 48.

Main amplifier signal path 44, which carries the main signal fromcoupler 36, includes a gain and phase adjuster GPA₁, a main amplifier 56and a delay element 60 that outputs to an output signal path 64. GPA₁includes a gain control input tap T₁, and a phase control input tap T₂,each of which can be steered so that GPA₁ operates to yield maximumsignal cancellation at the output of coupler 82 and the input of coupler104, as discussed below. The location in the circuit at which maximumsignal cancellation is to occur is sometimes referred to as the“cancellation node”.

Correctional amplifier signal path 48 which carries a sample, generatedby coupler 36, of the signal from input signal path 40 includes a delayelement 68, a gain and phase adjuster GPA₂ and a correctional amplifier74, the output of which connects to output signal path 64 via a coupler76. GPA₂ includes a gain control input tap T₃, and a phase control inputtap T₄, each of which can be steered so that GPA₂ is adjusted to requirea minimum, or near minimum, amount of power to be delivered to thecorrectional amplifier 74. As used herein, the terms “steer”, “steered”and “steering” are intended to comprise all suitable methods ofadjusting and/or controlling of the taps respective to a gain and phaseor other suitable adjuster. In the embodiment of the invention discussedbelow, taps T₁, T₂, T₃, and T₄, are steered by changing the voltagelevels applied to each of them respectively.

As will be apparent to those of skill in the art, GPA₂ and correctionalamplifier 74 form an error pathway 73 within amplifier portion 24.Accordingly, when the output of correctional amplifier 74 is coupled tothe output of delay 60, errors and pilot tones, if used, aresubstantially eliminated from the output signal path 64, such that theoutput signal path 64 presents a substantially linear amplification ofthe signal from input signal path 40.

Amplifier portion 24 is further characterized by a coupled path 79 thatinterconnects a first coupler 80, which is connected to the output ofmain amplifier 56, and a second coupler 82, which is connected to theoutput of delay element 68, in order to provide a sample of the errorintroduced by main amplifier 56 to the error pathway 73, commencing atGPA₂. Attenuation may be provided in coupled path 73, if not alreadyprovided by the first coupler 80.

The main amplifier signal path 44, the correctional amplifier signalpath 48, and the coupled path 79 together are sometimes referred to as a“signal cancellation loop”.

In the illustrated embodiment, amplifier portion 24 further includes apilot tone generator 86 that is coupled, via a coupler 90, to the inputof main amplifier 56. Pilot tone generator 86 generates a pilot tone foruse by error pathway 73 in the usual manner for reducing errorintroduced by main amplifier 56. By the same token, amplifier portion 24further includes a pilot tone receiver 94 that is coupled, via a coupler98, to output signal path 64. Pilot tone receiver 94 is operable tomeasure any remaining pilot tone present along output signal path 64 foreventual use by error pathway 73 to introduce a signal at coupler 76that will reduce the pilot tone in output signal path 64.

Detector-controller portion 28 connects to amplifier portion 24 throughvarious inputs and various outputs, as described herein. Specifically, acoupler 104 connected just prior to error pathway 73 delivers an inputsignal to a first detector D₁, which in turn presents a detector-outputto a gain controller C₁ and a phase controller C₂. In the illustratedembodiment, the detector-output is a measure of the amplitude of theenvelope of the input signal applied to it. However, it is within thescope of the invention to provide as a detector-output a signalproportional to the log of the RMS value of the envelope of the inputsignal or proportional to peaks of the envelope of the input signal, aswell as any other measure or signal that will occur to those skilled inthe art. Wherever in the following or in the claims that reference ismade to the detector-output being the amplitude of the envelope of theinput signal applied to it, it should be understood that such othersignals or measures are also intended.

Similarly, pilot tone receiver 94 delivers an output signal to a seconddetector D₂, which in turn presents a detector-output to a gaincontroller C₃ and a phase controller C₄. Again, detector D₂ outputs theamplitude of the envelope of the input signal applied to it. As will bediscussed in greater detail below, controllers C₁, C₂, C₃ and C₄ areoperable to steer taps T₁, T₂, T₃ and T₄, respectively, based on thesignals received from their respective detectors D, in order to findoptimum (or otherwise desired) gain and phase adjustments for each ofadjusters GPA₁ and GPA₂.

In the illustrated embodiment, tracer signals are applied to each ofmain amplifier signal path 44 and correctional amplifier signal path 48by using them to modulate the voltage levels applied to the taps T₁, T₂,T₃, and T₄, respectively. Those voltage levels are also referred to astap steering signals and the modulated voltage levels as modulated tapsteering signals. Each tracer signal, because it rapidly but slightlychanges either the gain or the phase in the signal cancellation loop,causes variations in the amplitude of the envelope of the input signalapplied to one of the detectors D₁ and D₂. The detected amplitudes ofthe envelopes of the signals applied to the detectors D₁ and D₂ arepassed to the respective controllers C. Each controller C extracts thevariation in the detector output caused by the tracer signal applied tothe corresponding tap and steers the tap accordingly. The variations inthe detector outputs caused by the tracer signals can be separated fromeach other because each tracer signal is selected to be orthogonal toeach other tracer signal. As described below, to achieve orthogonalityin the illustrated embodiment each tracer signal is a Walsh code, butother techniques, such as selecting appropriate pseudo noise sequencesas the tracer signals will be apparent to those of skill in the art. Aswill become apparent to those of skill in the art from the discussionherein, the present invention will operate with tracer signals that arenot totally orthogonal to each other, although better performance willbe obtained when using signals as orthogonal as possible. Accordingly,as used herein, the term orthogonal is intended to include bothperfectly orthogonal signals, such as Walsh codes, and near-orthogonalsignals, for example pseudo noise sequences taken over a time periodthat provides approximately orthogonal results. The general criterion isthat the more uncorrelated tracer signals are over an appropriate timeperiod the better the results.

Before going into the details, as an overview, consider an idealizedsituation that may help in understanding the embodiment of the inventiondescribed herein. To aid in understanding, we assume that the mainamplifier does not distort the input signal at all and we start withadjusting only one tap steering signal. We begin by setting a tapsteering signal at a particular voltage level. If that voltage level isapplied to a tap of an adjuster, a particular level of signalcancellation at the cancellation node results. If the voltage level isoptimal (so that the amplitude of envelope of the signal at thecancellation node is zero), dithering of the voltage level by a tracersignal that has an average value of zero (as do orthogonal and pseudonoise sequences over appropriate periods) will result in slightexcursions in the amplitude of envelope of the signal at thecancellation node above and below zero, but the sum of all theexcursions will be zero. Now suppose that the voltage level is notoptimal. Then the slight excursions in the amplitude of the envelope ofthe signal at the cancellation node will be to levels above and belowthe amplitude of envelope of the signal at the cancellation node thatwould occur if no dither were applied. The result will be a non-zero sumwith a polarity, or sign, the same as the polarity of the amplitude ofthe envelope of the signal at the cancellation node would be if nodither were applied. So far we have assumed that there is only one tap.If there are more taps, then by using orthogonal or pseudo noisesequences over appropriate periods as tracer signals, the excursions inthe amplitude of envelope of the signal at the cancellation node causedby dithering of each tap can be extracted separately from the amplitudeof envelope of the signal at the cancellation node, summed, and used toadjust the corresponding tap steering signals simultaneously.

Referring now to FIG. 2, detector-controller portion 28 will now bediscussed in greater detail. As shown, controllers C₁, C₂, C₃ and C₄each include the same components. Each controller C includes amultiplier 200 that receives a detector-output from a respectivedetector D. Controllers C are operable to utilize the detector-output todetermine how to steer their respective tap T. In the presentembodiment, each detector-output is the amplitude of the envelope of thesignal received by a respective detector D and carries combinedinformation about the effects of dithering (modulating) the respectivetap steering signals with the respective tracer signals on the amplitudeof the envelope of the signal received by the respective detector D. Theinformation carried about the effect of the dithering of each tapsteering signal with a tracer signal may be separately extracted fromthe detector-output in the manner discussed in greater detail furtherbelow.

To extract the effect of the tracer signal injected by tap T for thecontroller C, each multiplier 200 receives its Walsh code from a Walshcode generator 204. Each Walsh code generator 2041, 2042, 2043 and 2044,generates a unique Walsh code, which, as is understood by those of skillin the art, is a preselected pattern of one or more logical ones and/orlogical zeroes that repeat over a given period and is orthogonal to eachother Walsh code. As will be discussed in greater detail below, when thedetector-output from a respective detector D is multiplied by multiplier200 with a respective Walsh code, only the portion of thedetector-output resulting from the tracer signal injected at therespective tap T will be output from the respective multiplier 200.

Controllers C also each include an integrator 208 which is operable tosum the results from multiplier 200, which represent the effect oftracer signal for the respective tap T on the respectivedetector-output, for each period and output those summed results to anadjuster 212 which is operable to determine from the summed resultwhether the tap T it is responsible for is properly steered. If anadjuster 212 determines that its corresponding tap T was steered in theproper direction, then adjuster 212 outputs a signal that continues tosteer that tap T in the same direction. If adjuster 212 determines thatits corresponding tap T was steered in the wrong direction, thenadjuster 212 outputs a signal that steers that tap T in the oppositedirection. Adjuster 212 can also determine that the tap T is at anoptimum level, in which case adjuster 212 does not steer tap T at all,but leaves the tap steering signal at the existing level. Furtherdetails of adjuster 212 will be discussed in greater detail below.

To inject the tracer signal for a controller C into amplifier portion24, the signal outputted from adjuster 212 is modulated, using a summer216, with the Walsh code generated at Walsh code generator 204, theWalsh code having first been attenuated through an attenuator 220 by afactor A. The Walsh code is attenuated, by factor A, to a level thatprovides a suitable “dither” or “perturbance” that can be summed withthe control signal from adjuster 212 for the respective tap T. Thevoltage level of the resulting modulated signal is at a level that willgenerally yield a minimum reliably detectable signal at the output ofdetector D.

As will be apparent to those of skill in the art, in order for the Walshcode to behave as a good dither, each Walsh code for each controller Cis selected to have as many transitions as possible, while still beingorthogonal to the Walsh codes of the other controllers C. Also, as thetracer signal is averaged over a suitable period of time to reduce theeffects of noise in the detected signal, it is desired to choose a Walshcode, or other orthogonal signal, with a suitably long length. It ispresently preferred that a length for the Walsh codes is selected whichis at least twice the number taps T to be controlled, i.e.—in theembodiment of FIG. 1, the shortest desired length of Walsh codes wouldbe an eight chip code and, in fact, it is presently preferred to use aWalsh code length of sixty-four chips for a feed forward amplifier withfour taps T.

The output of each summer 216 is then presented to its respective tap T,thereby steering each respective tap T accordingly and injecting therespective tracer signal.

A method of controlling the gain and phase adjustment of feed forwardamplifier 20 will now be discussed with reference to FIG. 3. Theflow-chart in FIG. 3 shows a sequence of steps which can be used tooperate, for example, each controller C of detector-controller portion28, thereby steering each tap T. In other words, the sequence of stepsin FIG. 3 will be performed, in parallel, for each controller C.

Although, as mentioned above, in a presently preferred embodiment eachWalsh code is actually sixty-four chips in length, for simplicity whileexplaining the method, it will be assumed that each Walsh code W₁, W2,W₃ and W₄, is only eight chips in length. Each Walsh code W₁, W₂, W₃ andW₄ is generated by a respective Walsh code generators 204 ₁, 204 ₂, 204₃ and 204 ₄ and is shown in Table I and illustrated in thepulse-waveforms shown in FIG. 4. From the waveforms shown therein, it isto be understood that a “1” means a logical “1”, and “−1” means alogical “0”. TABLE 1 Chip W₁ W₂ W₃ W₄ 1 1 1 1 1 2 −1 −1 1 −1 3 −1 1 −1−1 4 1 −1 −1 1 5 −1 1 1 1 6 1 −1 1 −1 7 1 1 −1 −1 8 −1 −1 −1 1

Again for simplicity, the method of FIG. 3 will only be discussed indetail with reference to controllers C₁ and C₂ and their associateddetector D₁. The method begins at step 300 where a signal is detected atdetector D₁ from the amplifier portion 24 of feed forward amplifier 20.To illustrate how this step can be accomplished according to a presentembodiment, it will be assumed that feed forward amplifier 20 has justbeen activated (i.e. initialized), but that no input signal is presentalong input signal path 40, and accordingly no output signal is presentalong output signal path 64.

The activity in feed forward amplifier 20 at this point in the method isillustrated in FIG. 5, where detector D₁, controller C₁ and controllerC₂ are shown. As there is no input signal along input signal path 40,detector D₁ detects this and outputs a corresponding waveform, which isrepresented in FIG. 5 as a detector-output waveform 400 a, which in turnis inputted into multiplier 200 ₁ and multiplier 200 ₂.

By way of further background to the operation of the present embodiment,it will be apparent to those of skill in the art that the tracer signalbeing applied to the taps T of gain and phase adjuster GPA₁, whether aWalsh code or any other dither, will only be detectable at detector D₁where there is an input signal along input signal path 40 as the tracersignal is a modulation of the input signal. Similarly, if a pilot toneis being injected at coupler 90, then the tracer signal applied at thetaps T of GPA₂ will be detectable at detector D₂ as modulation of thepilot tone detected at detector D₂. As there is as yet no input signalin FIG. 5, detector-output waveform 400 a is all zeros, as shown.

Referring again to FIG. 3, the method then advances to step 320 wherethe tracer signal for the tap T₁ respective to the controller C₁ isextracted from the signal detected at step 300. In a present embodiment,this signal is extracted from detector-output waveform 400 a usingmultiplier 200 and integrator 208. First, multiplier 200 multiplies theWalsh code output from Walsh code generator 204 with the detector-outputwaveform 400 a to extract the tracer signal. The product waveform ispresented to integrator 208, which sums each pulse in the waveform overthe number of chips in the Walsh code. The outputs for each integrator208 ₁, 208 ₂ are represented on FIG. 5 as items 404 a ₁ and 404 ₂,respectively.

Specifically, for controller C₁, since the detector-output 400 a={0, 0,0, 0, 0, 0, 0, 0}, and since the output of Walsh code generator 204 ₁can be represented by the series W₁={1, −1, −1, 1, −1, 1, 1, −1}, thenthe output of multiplier 200 ₁ can be represented as {0, 0, 0, 0, 0, 0,0, 0}.times. {1, −1, −1, 1, −1, 1, 1, −1}=(0, 0, 0, 0, 0, 0, 0, 0). Theresult 404 a ₁, from integrator 208, can be represented as 404 ₁=(0, 0,0, 0, 0, 0, 0, 0)=0.

Similarly, for controller C₂, since detector-output 400 a={0, 0, 0, 0,0, 0, 0, 0} and since the output of Walsh-code generator 2042 can berepresented by the series W₂={1, −1, 1, −1, 1, −1, 1, −1}, then theoutput of multiplier 2002 can be represented as {0, 0, 0, 0, 0, 0, 0,0}.times. {1, −1, 1, −1, 1, −1, 1, −1}=(0, 0, 0, 0, 0, 0, 0, 0). Theresult 404 a ₂, from integrator 2082 can be represented as 404 a ₂=(0,0, 0, 0, 0, 0, 0, 0)=0.

Referring again to FIG. 3, the method then advances to step 340 wherethe appropriate steering signal for the tap T_(i) respective to a givencontroller C_(i) is determined. In the present embodiment, this step isperformed by adjuster 212. Continuing with the above example beingdiscussed with reference to FIG. 5, the result 404 a from eachintegrator 208 is then passed to its respective adjuster 212. As shownin the example of FIG. 5, the result 404 a from each integrator 208 was“0”, and this value is passed to adjuster 212.

In the present embodiments, adjuster 212 includes digital signalprocessing circuitry that is operable to make the determination ofwhether and how to steer the tap T based on the result 404 a passed fromits respective integrator 208. Adjuster 212 determines from the received“0” input that no steering of a tap T is required and the methodadvances to step 360, wherein no adjustment is made to the steeringsignal applied to the respective tap T.

If adjuster 212 had received a positive or negative input from theresult 404 a, then an appropriate adjustment to the tap steering signalwould be determined and the method would have advanced to step 360 wherethe appropriate adjustment of the steering signal is applied to therespective tap T.

Continuing with the example being discussed in conjunction with FIG. 5,as it was determined at step 340 that no adjustment to the steeringsignal was required, and as feed forward amplifier 20 has just beenactivated, adjuster 212 determines that the tap T for its respectivecontroller C should remain in its nominal position. Each adjuster 212then outputs a corresponding tap steering signal, indicated on FIG. 5 assignals 408 a, and 408 a ₂. The exact format of tap steering signals 408can be generated using known means and circuitry and need onlycorrespond with the format required to control the specific type of gainand phase adjusters used within amplifier portion 24.

Tap steering signals 408 a are then presented to their respective summer216, which sums the tap steering signal 408 a with an attenuated versionAW of the Walsh code W. This attenuated Walsh code is indicated on FIG.5 as items AW₁ and AW₂ and is the tracer signal to be injected in thesignal paths of amplifier portion 24 for the next iteration of thecontrol method. It will be apparent to those of skill in the art thatthe factors A for each attenuator 220 can differ from each other.Attenuated Walsh codes AW are attenuated by factors A to a level,appropriate for the specific GPA employed, so they act as a “dither”modulated on top of its tap steering signal 408 a and that operation ofthe gain and phase GPA is not impeded by the dither.

Attenuated Walsh codes AW are produced by attenuators 220, which simplyreceive the output of their respective Walsh code generator 204 andgenerate and output an attenuated version thereof to their respectivesummers 216. Thus, each tap steering signal 408 a and respectiveattenuated Walsh code AW are combined by their respective summer 216, tocreate a dithered tap steering signal, indicated on FIG. 5 as items 412a ₁ and 412 a ₂. At step 360, the dithered tap steering signals 412 a ₁,412 a ₂ are then presented to their respective taps T₁, T₂ of GPA₁ andthe method then returns to step 300, where another iteration of themethod begins.

As mentioned above, the method shown in FIG. 3 operates simultaneouslyfor detector D₂ and controllers C₃ and C₄ in the same manner as thatdescribed above for detector D₁ and controllers C₁ and C₂. Thus,steering adjustments can be effected at each tap T at the same time.

An example of a second iteration through the method of FIG. 3 will nowbe discussed with reference to FIG. 6. It is assumed that, prior to thisiteration an input signal is being input along input signal path 40.FIG. 6 again shows detector D₁ and controllers C₁ and C₂. This iterationcommences with step 300 again being performed by detector D₁. As thereis now an input signal along input signal path 40, detector D₁ nowdetects the tracer signal (dither) that has been applied to at least oneof the gain and phase adjusters and reflects this detection indetector-output waveform 400 b. For purposes of explaining the presentembodiment, it will be assumed that detector-output waveform 400 b is{−3, −1, 0, 2, −3, 0, −1, 1} and waveform 400 b is input to multipliers200 ₁ and 200 ₂.

Referring again to FIG. 3, the method then advances to step 320 wherethe tap measurement for the tap T_(i) respective to the controller C_(i)is extracted from the signal detected at step 300. In the presentexample discussed in conjunction with FIG. 6, this signal is extractedfrom detector-output waveform 400 b using multiplier 200 _(i) andintegrator 208 _(i) of each controller C_(i). First, multiplier 200multiplies the Walsh code output from Walsh code generator 204 with thedetector-output waveform 400 b. The product waveform is then presentedto integrator 208, which sums each pulse in the waveform over the numberchips in the Walsh code. The results from each integrator 2081, 2082 arerepresented on FIG. 6 as items 404 b ₁ and 404 b ₂, respectively.

Specifically, for controller C₁, since the detector-output 400 b={−3,−1, 0, 2, −3, 0, −1, 1}, and since the output of Walsh-code generator204 ₁ W₁={1, −1, −1, 1, −1, 1, 1, −1}, then the output of multiplier 200₁ can be represented as {−3, −1, 0, 2, −3, 0, −1, 1}.times.{1, −1, −1,1, −1, 1, 1, −1}=(−3, 1, 0, 2, 3, 0, −1, −1). The result for integrator208, can be represented as 404 b ₁=(−3, 1, 0, 2, 3, 0, −1, −1)=1.Similarly, for controller C₂, 400 b={−3, −1, 0, 2, −3, 0, −1, 1} andsince the output of Walsh-code generator 204 ₂ W₂={1, −1, 1, −1, 1, −1,1, −1}, then the output of multiplier 2002 can be represented as {−3,−1, 0, 2, −3, 0, −1, 1}.times.{1, −1, 1, −1, 1, −1, 1, −1}=(−3, 1, 0,−2, −3, 0, −1, −1). The result for integrator 2082 can be represented as404 b ₂=(−3, 1, 0, −2, −3, 0, −1, −1)=−9.

The method then advances to step 340 where the appropriate steeringsignal for the tap T respective to a given controller C is determined.Continuing with the above example being discussed with reference to FIG.6, the result 404 b for each integrator 208 is then passed to itsrespective adjuster 212. In this example, the result 404 b ₁ produced byintegrator 208 ₁ was “1” and this value is passed to adjuster 212 ₁. Theresult 404 b ₂ produced by integrator 2082 was “−9”, and this value ispassed to adjuster 212 ₂. In each case, the sign of the integratoroutput determines which way the respective tap T is adjusted.

As previously discussed, adjusters 212 include digital signal processingcircuitry which is operable to make the determination of whether tosteer the tap T based on the result 404 b passed from its respectiveintegrator 208. In the present embodiment, adjusters 212 are configuredso that, if the received input from its respective integrator 208 doesnot equal “0”, then it is determined that steering of its respective tapT is required. Accordingly, in the example of FIG. 6 adjusters 212 ₁ and212 ₂ both determine that steering of the respective taps T₁, T₂ isrequired.

For controller C₁, adjuster 212 ₁ has received a “1”, and therebydetermines that the tap steering signal 408 b, to tap T₁ should beincreased and accordingly, the output tap steering signal 408 b ₁ isincreased by a preselected increment from the previous signal that wasused during the previous iteration through the method of FIG. 3. Forcontroller C₂, adjuster 212 ₂ has received a “−9”, and therebydetermines that the tap steering signal 408 b ₂ to tap T₂ should bedecreased and accordingly, the output tap steering signal 408 b ₂ isdecreased by a preselected increment from the previous signal that wasused during the previous iteration through the method of FIG. 3. Tapsteering signals 408 b are then presented to their respective summer216, which sums the tap steering signal 408 a with the respectiveattenuated Walsh code AW. Thus, each tap steering signal 408 a andattenuated Walsh code AW are summed together by their respective summer216, to create a dithered tap steering signal, indicated on FIG. 6 asitems 412 b ₁ and 412 b ₂. The dithered tap steering signals 412 b arethen presented to their respective taps T of their respective GPA atstep 360.

Iterations through the method of FIG. 3 repeat continuously for eachcontroller C, increasing or decreasing each tap output signal 412 untilan optimum level for a respective tap T is reached, at which point therespective controller C simply maintains the tap output signal 412 atits current level (i.e.—the result from integrator 208 of the productfrom multiplier 200 of waveform 400 and Walsh code W is “0”) until,during a subsequent iteration through the method of FIG. 3, furthersteering of the respective tap T is required.

While the embodiments discussed herein are directed to specificimplementations of the invention, it will be understood thatcombinations, sub-sets and variations of the embodiments are within thescope of the invention. For example, it will now be apparent to those ofskill in the art that amplifier portion 24 is a substantially knownconfiguration for one type of amplifier portion of a feed forwardamplifier, yet other configurations of amplifier portion 24 are withinthe scope of the invention. Other such configurations are discussed in aco-pending U.S. patent application Ser. No. 09/715,085, assigned to theassignee of the present invention, the contents of which areincorporated herein by reference. In particular, this applicationteaches a feed forward amplifier with a single pilot tone generatorreceiver, which is also suitable for incorporation into the presentinvention. A general discussion of feed forward amplifiers instructiveto those of skill in the art for the design of amplifier portions isdiscussed in U.S. Pat. No. 3,471,798, the contents of which are alsoincorporated herein by reference.

As will also be apparent to those of skill in the art, feed forwardamplifiers can include more than two gain and phase adjusters. In such acase, a detector-controller circuit can be employed for each gain andphase adjuster and a separate orthogonal tracer signal employed for eachtap T.

Further, while the embodiments discussed herein refer specifically toFFAs having a pilot tone, it is to be understood that the presentinvention is also applicable to FFAs that do not use pilot tone, but usesome other method, for example such as measuring intermodulation energyat detector D₂.

While the embodiments discussed herein refer to gain and phase adjustershaving gain and phase taps T, it is to be understood that the presentinvention is not so limited and can be applied to other types ofadjusters, such as phase and gain adjusters having in phase ‘T’ andquadrature “Q” taps. Furthermore, while the embodiments discussed hereinrefer to controlling gain and phase adjustments in FFAs, it is to beunderstood that the apparatus and method discussed herein can bemodified for use with any appropriate circuit where adaptive control isused, such as feed forward circuits, etc.

It is also to be understood that while the embodiments discussed hereinrefer to Walsh codes, any type of orthogonal tracer-signal, such assuitable length pseudo noise sequences or the like can be used, withappropriate modifications to other aspects of the remainder of thecircuit. Additionally, while the number of chips of the Walsh codes usedin the exemplary embodiments discussed herein corresponds to the periodof the pulse wave-form of the detector-output, it will be understoodthat these periods need not correspond at all. In general, it is to beunderstood that any means or method for extracting a particular tapmeasurement from a detector-output can be used, such as using frequencydivision multiplexing.

While presently less preferred due to increased complexity, it iscontemplated that the magnitude of the output of integrator 208 couldalso be used to provide further information to determine the amount bywhich each tap T is to be steered, in addition to using the polarity ofthe integrated signal to determine the direction the tap T should besteered. In such a case, instead of adjusting the amount by apreselected increment, a variable increment can be selected dependingupon the magnitude of the output.

It is also contemplated that the size of the increment can vary, in apreselected manner, between start up of the adaptive circuit and normaloperation of the adaptive circuit. For example, at start up and for agiven number of iterations, amplifier 20 of FIG. 1 can employ anincrement/decrement size of 5 units, followed by an increment/decrementsize of 3 units for another given number of iterations, then followed byan increment/decrement size of 2 units for another given number ofiterations, after which an increment/decrement size of 1 unit isemployed. This should allow faster convergence of the amplifier at startup.

The present invention provides a novel feed forward amplifier thatincludes a method and apparatus for steering the gain and phaseadjustment such that each tap within the gain and phase adjusters isadjusted at substantially the same time to converge towards an optimumoperating setting. Convergence towards the optimum settings aretherefore obtained substantially faster and/or more accurately thanprior art feed forward amplifiers. Each tap can have a tracer signal,which is orthogonal to other tracer signals, applied to the signal pathsthrough the amplifier. The respective tap measurement is extracted andemployed by each tap controller to appropriately alter the respectivetap steering signal.

The above-described embodiments of the invention are intended to beexamples of the present invention and alterations and modifications maybe effected thereto, by those of skill in the art, without departingfrom the scope of the invention which is defined solely by the claimsappended hereto.

1. A circuit having a node at which a signal is adaptively minimized bythe circuit, comprising: a controller providing an output voltage level,the output voltage level modulated by a low level signal that takes on apreselected sequence of values over a preselected period; an adjusterconnected to the output of the controller for providing a controlledchange in a characteristic of the adaptive circuit that results in achange in the envelope of the signal at the node, the magnitude of thechange in the characteristic controlled by the voltage level presentedto the adjuster by the controller; and a detector, the input of which isconnected to the node and the output of which is connected to thecontroller, the detector outputting a measure of the envelope of thesignal at the node, wherein after the preselected period a new settingfor the voltage level presented to the adjuster by the controller isobtained by multiplying the detector output by the low level signal,summing the resulting series of values, and changing the voltage levelpresented to the adjuster in accordance with the value of the sum. 2.The circuit of claim 1, wherein the output voltage level is increased ordecreased depending upon the polarity of the sum.
 3. The circuit ofclaim 1, wherein the output voltage level is left unchanged if the sumis zero or within a preselected range about zero but, if the sum isoutside the preselected range about zero, increasing or decreasing theoutput voltage level depending upon the polarity of the sum.
 4. Thecircuit of claim 3, wherein the output voltage level is increased if thesum is positive and decreased if the sum is negative.
 5. The circuit ofclaim 3, wherein the low level signal voltage level is changed inproportion to a magnitude of the sum.
 6. The circuit of claim 5, whereinthe low level signal is chosen to be a Walsh code.
 7. The circuit ofclaim 5, wherein the low level signal is chosen to be a pseudo noisesequence.